lightning input validation

aura-input-validation.js

({
  validateForm: function(cmp) {
    // Get All lightning:input elements with aura:id "input"
    var inputs = cmp.find("input");

    // Iterate over array of input components
    // `acc` is a local variable, defined as a boolean in this case
    // `input` is the input component during iteration
    var isValid = inputs.reduce(function(acc, input) {
      input.showHelpMessageIfInvalid();
      return acc && input.get("v.validity").valid;
    }, true); // acc starts as true

    return isValid;
  }
})

lwc-input-validation.js

validate () {
  const requiredInputs = this.template.querySelectorAll('.required')
  const isValid = [ ...requiredInputs ].reduce((validity, el) => {
    const report = el.reportValidity()
    return validity && report
  }, true)
  return isValid
}